comp-undo-steps 0: Example step implementation

comp-undo-steps-0-step-example.js

function stepA(options) {
  return (next) => async (pctx) => {
    // Do stuff, allowing any errors to reject this promise,
    // passing them back to previous steps.
    const result = await doSomething(pctx.foo);
    const nextPctx = { ...pctx, bar: result };

    try {
      // NOTE: Technically, you could further process the result
      // before returning it.
      return await next(nextPctx);
    }
    catch (error) {
      // Undo stuff.  If an error occurs here, it will still result
      // in previous steps trying to undo themselves.
      // If an undo step errors, combine the errors in some manner
      // so we don't lose debug info.
      try {
        await undoSomething(pctx.foo);
      }
      catch (undoError) {
        throw combineErrors(error, undoError);
      }

      // If undo was a success, propagate the error back.
      throw error;
    }
  };
}